Upper Yellowstone and Madison River Basins
April 1997

Snow
Snow just keeps collecting at record levels this year.
Average snow water equivalent (SWE) is about 63 percent
above normal in the Madison drainage and 58 percent above
average in the Yellowstone River drainage. The Madison
drainage SWE is about 30 percent ahead of last year at this
time. SWE in the Yellowstone drainage is nearly 14
percent more than last March. The graph below indicates
the basin is well above previously recorded snow levels.
See the snow course basin summary at the beginning of this
document for more details on specific sites.

Precipitation
March precipitation in the Madison and Yellowstone
drainage was about 40 percent above average and 3 percent
below last March. Water year-to-date precipitation is about
17 percent ahead of last year and 57 percent above average.
Four stations were used to compute the averages.

Reservoir
Reservoir storage is below normal for the reporting
reservoirs. Ennis Lake is about 15 percent below average
(28,200 acre feet) and Hebgen Lake's current storage is
about 5 percent below normal (234,400 acre feet). Ennis
Lake is storing 69 percent of its capacity, while Hebgen
Lake is storing 62 percent of capacity. See reservoir
storage on the following page for details.

Streamflow
The 50 percent chance runoff is expected to be 42 to 56
percent above average for the April through September
runoff period. Yellowstone at Corwin Springs has a 50
percent chance of yielding about 3,000,000 acre feet (55
percent above normal). Yellowstone near Livingston has a
50 percent chance of yielding about 3,500,000 acre feet (56
percent above normal). Madison River near Grayling has a
50 percent chance of yielding about 690,000 acre feet (42
percent above normal). See the following page for detailed
runoff volumes.